Airports are becoming increasingly necessary near urban areas to address the needs of commuters and other travel between cities. However, airports occupy a large footprint due to long runways and expansive air space needed for fixed wing aircraft to safely takeoff and land. Constructing such airports is also cost prohibitive for small and medium sized municipalities. Where large cities are better situated to afford the construction of airports, the noise, pollution and safety issues presented by urban airports is problematic. Accordingly, there is a long-felt need in the aviation industry for small, affordable, vertical takeoff and landing (VTOL) aircraft that may takeoff, land, and be stored, on relatively small parcels of commercial and residential real estate.
Historically, the aviation industry believed that helicopters would fulfill the need for small, affordable, VTOL aircraft. Unfortunately, helicopters remain a special-purpose aircraft due to their control systems, their large-diameter rotors, and their slow speed and limited range. Helicopter control systems include complex mechanisms for continuously adjusting the rotor pitch. Such control systems are expensive to construct and to maintain. Moreover, helicopters are notoriously difficult to fly, requiring specialized flight training, particularly as compared to fixed-wing aircraft. Further, the large-diameter exposed rotors present serious safety and operational challenges. Helicopters also suffer from their limited ability to fly anywhere near the speed and range of fixed-wing aircraft. Accordingly, traditional helicopter technology is ill suited to address important operational and user needs and demands.
Over the decades, there have been numerous attempts to combine the speed, range and comfort of a fixed-wing airplane with the VTOL and hover capability of a helicopter. However, except for two military aircraft, the British Harrier jet and the U.S. Air Force F-35, the tiltrotor category of aircraft is the only combined VTOL/fixed-wing aircraft which appears to be near FAA certification and commercial production. However, tiltrotors can only lift off and land vertically because the rotor blades would strike the ground in the forward flight configuration. Therefore, the gross weight of a tiltrotor aircraft is less than fixed-wing aircraft, which are capable of taking off on a runway. The large engine/rotor assemblies also diminish the aerodynamics of the wings to which they are secured. While this reduces performance, it further decreases safety where an emergent gliding landing is necessary. This is particularly problematic in tiltrotor aircraft where a gliding landing becomes necessary shortly after takeoff when the rotors are positioned vertically, and a “tilt-wing” aircraft when the rotors and wings are positioned vertically. Further, because of its size and complexity, the tiltrotor could not be the basis (from a physical or engineering standpoint) for a light, fast, compact, and affordable aircraft in the commercial market.
There is another category of VTOL aircraft designed to reach high speeds—that is, helicopters with additional components to increase speed, such as propellers, known as “compound helicopters.” Sikorsky's X2 technology aircraft and AVX Aircraft Company's coaxial rotor/dual ducted fan technology are included in this category. The Sikorsky and AVX aircraft are not in commercial production, but are designed to be capable of achieving high speed with VTOL and hovering capability superior to any fixed-wing aircraft except the tilt-rotor. However, similar to the tilt-rotor, these compound helicopters have standard large helicopter blades for lift during take-off and landing, rather than smaller safer ducted fans for lift during take-off and landing. Various prototype or experimental aircraft with rotating ducted fans were flown in the mid-20th century. However, the engines and fans didn't provide sufficient lift for cargo or passengers, and those aircraft experienced significant controllability problems.
Many of these prior art VTOL aircraft designs suffer a wide array of similar disadvantages that have prevented their wide-spread acceptance as a day-to-day commuter aircraft. Another disadvantage is that many such designs require several times the horsepower to maintain the aircraft aloft, in takeoff and hover modes. Accordingly, such aircraft suffer from relatively high rates of fuel consumption, both while hovering and in forward, horizontal flight.